yes, you can.
goto tooloptionscolor tabmodify buttoncustom tab
here you can create you own custom colors.
you are limited to 56 total.

-----Original Message-----
I'm trying to shade cells in an Excel sheet. However,
there are only a few
colors to choose from and they're all quite
dark/unattractive. How do I get
more customized colors? I see it is possible to "mix" by
using patterns, but
that's quite clumsy I think. Are there any other methods
of adding new
colors?
.